The demand on multimedia applications such as video streaming and Internet Protocol Television (IPTV) over wireless communications has dramatically increased in recent times. A fixed multimedia base rate for transmission over such wireless communications is generally undesirable due to wireless channel conditions that fluctuate much more than wired links, and the resulting low perceptive quality due to service outages.
One way in which to improve the reliability of the transmission of multimedia information between a transmitter and receiver over a wireless network is to implement a coding technique. Examples of coding techniques include multiple description coding (MDC) and successive refinement coding (SRC). In MDC, the video signal is encoded into multiple descriptions at different source coding rates. Each description can be decoded independently, and a better quality of video can be achieved when more descriptions are received correctly. In SRC, the video signal is encoded into multiple layers at different source coding rates, i.e. base and several enhancement layers. At the receiver, an enhancement layer is decoded and successively refines the description in the previous enhancement or base layers as long as the previous layers are received correctly. An example layered coding technique is disclosed for point-to-point Single-Input Single-Output (SISO) and Multiple-Input Multiple-Output (MIMO) systems in “Source and channel coding for quasi-static fading channels,” by D. Gündüz and E. Erkip, Proc. Asilomar Conf. on Signals, Systems and Computers, Pacific Grove, Calif., November 2005, pages 18-22.
Assuming that the channel state information (CSI) is available at the receiver but not at the transmitter, in a slow-fading scenario, once a channel is in deep fade, coding no longer helps to increase the reliability of the transmission. In such cases, the natural performance measure becomes the outage probability, which is the probability when the maximum supportable rate is lower than the fixed transmission rate R. Therefore, the performance metric of layered video transmission over wireless communications becomes the expected video distortion. Accordingly, it has become increasingly important to minimize the expected video distortion.
An alternative development to mitigate the undesired effects of fading is by way of diversity techniques, such as antenna diversity and cooperative diversity.
Unlike an antenna diversity system, which employs multiple antennas at the receiver and/or the transmitter, a cooperative diversity system utilizes a relay without requiring multiple antennas at each terminal. A. Sendonaris, E. Erkip, and B. Aazhang in “Source and channel coding for cooperative relaying,” IEEE Trans. Inf. Theory, vol. 53, no. 10, pages 3454-3475, October 2007, proposed cooperative source and channel coding using a system consisting of one source node, one relay node and one destination node. The cooperative technique in that proposal related to the single relay node assisting a direct link communication between the source and destination nodes.